System and method for preventing telephone line blocking by a modem

Abstract

A modem includes a Digital Access Arrangement (DAA) Circuit and modem software that is executed by a processor. When the DAA Circuit detects that the modem software is nonfunctional, it enters an on-hook state to prevent blocking of a coupled telephone line. A nonfunctional state of the modem software is detected when the modem software ceases to interact with the DAA Circuit in an expected manner. In a first operation, the nonfunctional state is determined when the modem software does not reset a count down timer in the DAA Circuit before the count down timer reaches a termination value. In a second operation, the nonfunctional state is determined when the modem software does not access the DAA Circuit before the count down timer reaches the termination value. In a third operation, the nonfunctional state is determined when the modem software ceases writing transmit data to DMA memory.

1. A method for preventing a modem that includes a Digital Access Arrangement (DAA) Circuit and modem software from blocking a telephone line when the modem software becomes nonfunctional, the method comprising:
 establishing, by the modem, a communication across the telephone line with a remote modem;  
 servicing, by the modem, the communication across the telephone line with the remote modem;  
 detecting, by a Digital Access Arrangement (DAA) Circuit of the modem, that the modem software of the modem has become nonfunctional with respect to the communication; and  
 releasing, by the DAA Circuit, the telephone line when it determines that the modem software has become nonfunctional with respect to the communication.  
 
     
     
       2. The method of  claim 1 , wherein the modem software is executed by a device that is selected from the group consisting of at least a digital computer, a modem card, an external modem, a FAX machine, and a set top box. 
     
     
       3. The method of  claim 1 , wherein detecting, by the DAA Circuit, that the modem software has become nonfunctional with respect to the communication further comprises:
 setting a count down timer upon access of the DAA Circuit by the modem software; and  
 determining that the modem software has become nonfunctional when the count down timer reaches a termination value.  
 
     
     
       4. The method of  claim 3 , wherein the DAA Circuit resets the count down timer when the modem software accesses the DAA Circuit. 
     
     
       5. The method of  claim 3 , wherein the modem software resets the count down timer when the modem software accesses the DAA Circuit. 
     
     
       6. The method of  claim 3 , wherein the count down timer is reset each time that the modem software writes data to the DAA Circuit. 
     
     
       7. The method of  claim 3 , wherein the count down timer is reset each time that the modem software reads data from the DAA Circuit. 
     
     
       8. The method of  claim 1 , further comprising:
 writing transmit data and an on-hook command to Direct Memory Access (DMA) memory by the modem software;  
 reading the transmit data from the DMA memory by the DAA Circuit; and  
 determining that the modem software has become nonfunctional when the DAA Circuit reads the on-hook command from DMA memory.  
 
     
     
       9. The method of  claim 8 , wherein each time that the modem software writes transmit data to the DMA memory, the modem software overwrites a previously written on-hook command with transmit data and writes a new on-hook command immediately following currently written transmit data. 
     
     
       10. The method of  claim 1 , wherein the DAA Circuit detects that the modem software has become nonfunctional with respect to the communication when the modem software fails to access the DAA Circuit after a period of time. 
     
     
       11. A modem comprising:
 modem software that is executed by a processor;  
 a Digital Access Arrangement (DAA) circuit communicatively coupled to the modem software, the DAA Circuit also coupled to a telephone line; and  
 wherein the DAA Circuit: 
 establishes a communication across the telephone line with a remote modem in conjunction with the modem software;  
 services the communication across the telephone line with the remote modem in conjunction with the modem software;  
 detects that the modem software has become nonfunctional with respect to the communication; and  
 releases the telephone line when it determines that the modem software has become nonfunctional with respect to the communication.  
 
 
     
     
       12. The modem of  claim 11 , wherein the processor is resident within a host device that is selected from the group consisting of at least a digital computer, a modem card, an external modem, a FAX machine, and a set top box. 
     
     
       13. The modem of  claim 11 :
 further comprising a count down timer;  
 wherein the count down timer is set to an initial value upon access of the DAA Circuit by the modem software; and  
 wherein the DAA Circuit determines that the modem software has become nonfunctional when the count down timer reaches a termination value.  
 
     
     
       14. The modem of  claim 13 , wherein the DAA Circuit resets the count down timer when the modem software accesses the DAA Circuit. 
     
     
       15. The modem of  claim 13 , wherein the modem software resets the count down timer when the modem software accesses the DAA Circuit. 
     
     
       16. The modem of  claim 13 , wherein the count down timer is reset each time that the modem software writes data to the DAA Circuit. 
     
     
       17. The modem of  claim 13 , wherein the count down timer is reset each time that the modem software reads data from the DAA Circuit. 
     
     
       18. The modem of  claim 13 :
 wherein the DAA Circuit further comprises a Direct Memory Access (DMA) engine that accesses a DMA memory of the host device;  
 wherein the modem software writes transmit data and an on-hook command to the DMA memory;  
 wherein the DMA engine of the DAA Circuit reads transmit data from the DMA memory; and  
 wherein the DAA Circuit determines that the modem software has become nonfunctional when the DMA engine of the DAA Circuit reads the on-hook command from DMA memory.  
 
     
     
       19. The modem of  claim 18 , wherein each time that the modem software writes transmit data to the DMA memory, the modem software overwrites a previously written on-hook command with transmit data and writes a new on-hook command immediately following currently written transmit data. 
     
     
       20. The modem of  claim 11 , wherein the DAA Circuit detects that the modem software has become nonfunctional with respect to the communication when it fails to access the DAA Circuit after a period of time. 
     
     
       21. A method for preventing a modem that includes a Digital Access Arrangement (DAA) Circuit and modem software from blocking a telephone line when the modem software becomes nonfunctional, the method comprising:
 establishing, by the modem, a communication across the telephone line with a remote modem;  
 servicing, by the modem, the communication across the telephone line with the remote modem;  
 setting a count down timer upon each access of the DAA Circuit by the modem software;  
 determining, by the DAA Circuit, that the modem software has become nonfunctional when the count down timer reaches a termination value; and  
 releasing, by the DAA Circuit, the telephone line when it determines that the modem software has become nonfunctional with respect to the communication.  
 
     
     
       22. The method of  claim 21 , wherein the DAA Circuit resets the count down timer each time that the modem software writes data to the DAA Circuit. 
     
     
       23. The method of  claim 21 , wherein the DAA Circuit resets the count down timer each time that the modem software reads data from the DAA Circuit. 
     
     
       24. The method of  claim 21 , wherein the modem software resets the count down timer each time that it writes data to the DAA Circuit. 
     
     
       25. The method of  claim 21 , wherein the modem software resets the count down timer each time that it reads data from the DAA Circuit. 
     
     
       26. A method for preventing a modem that includes a Digital Access Arrangement (DAA) Circuit and modem software from blocking a telephone line when the modem software becomes nonfunctional, the method comprising:
 establishing, by the modem, a communication across the telephone line with a remote modem;  
 servicing, by the modem, the communication across the telephone line with the remote modem;  
 reading transmit data from a DMA memory servicing the modem by the Digital Access Arrangement (DAA) Circuit of the modem;  
 determining, by the DAA Circuit, that the modem software has become nonfunctional when the DAA Circuit reads an on-hook command from DMA memory; and  
 releasing, by the DAA Circuit, the telephone line when the DAA Circuit determines that the modem software has become nonfunctional with respect to the communication.  
 
     
     
       27. The method of  claim 26 , wherein each time that the modem software writes transmit data to the DMA memory, the modem software overwrites a previously written on-hook command with transmit data and writes a new on-hook command immediately following currently written transmit data.